The rise of mobile Internet applications has brought about new challenges and requirements, e.g., higher user rate and more flexible communication mode, for the existing mobile communication technology.
New radio technologies, such as Device to Device (D2D) communication technology or enhanced Local Access (eLA) technology, have been developed to meet these requirements.
Different from any previous mode where the communication is merely performed in a mobile communication network via a link between a user and a base station, the D2D communication technology tries to perform the communication via a direct radio link between the users, while the eLA technology tries to set a local access node with a low power and then performs the communication via a radio link between the user and the local access node. Generally, the link between the users or between the user and the local access node has a short transmission distance and a high link quality, and can provide a high frequency reuse gain. As a result, it can help to ease the problems of constrained spectrum resources of a macro cell as well as low user rate.
In order to realize the communication between the users or between the user and the local access node, at least one of the users or the local access node must at first discover the other neighboring users, and then establish a connection with the discovered user for communication. Different from the base station in the existing mobile communication, the user or the local access node will not transmit a sync signal or a reference signal periodically to help the user to identify a cell ID. Thus, it is necessary to design a scheme so as to discover the neighboring users by the user or the local access node.
An existing method for discovering a UE is realized by setting a specific physical layer channel, which occupies certain time-frequency resources and is dedicated to identify a neighboring UE. For example, a UE will use the specific physical layer channel to broadcast a signal including its ID information, while the other neighboring UE will monitor the specific physical layer channel, receive a discovering signal and recover a UE ID included therein. In other words, the UE that transmits the broadcast signal will be discovered.
However, such a method needs to occupy certain time-frequency resources for discovering the UE, and these resources cannot be used for data transmission, so a fixed overhead of a system will be increased. In addition, a new physical layer channel introduced into the existing system will certainly have a significantly impact thereon.